Technical Field
The present disclosure relates to an angle detecting apparatus and an angle detecting system using a resolver.
Background
As an angle detecting apparatus capable of detecting an angle with high sensitivity, which can be manufactured through a very simple assembly process without requiring complicated processing, an angle detecting apparatus is known, which includes: a rotor formed of a disk member made of a magnetic material having a uniaxial magnetic anisotropy, the disk member being rotatable around a central point in a plane of the disk member; a stator which has substantially the same outer shape as that of the disk member of the rotor and is provided to face the surface of the disk member of the rotor, the stator being divided into a plurality of fan-shaped parts, an exciting coil or a detection coil being wound around along an outer periphery of each divided part; and a back yoke which has substantially the same outer shape as that of the disk member of the stator and is provided to face the disk member of the stator, the back yoke being provided on a side opposite to a side where the rotor is provided with the stator interposed therebetween (see for example WO 2012/002126 A1).
FIGS. 1A to 1C show an angle detecting apparatus in accordance with WO 2012/002126 A1 including: a rotor 5 composed of a disk member having a uniaxial magnetic anisotropy, the rotor 5 being rotatable in a plane of a disk member around a central point 5a to which a rotation shaft 6 is connected; a stator 3 which has substantially the same outer shape as that of the disk member of the rotor 5 and is provided to face the disk member of the rotor 5 in a noncontact manner; and a back yoke 2 which is formed of a magnetic thin plate having no orientation (isotropic) and has substantially the same outer shape as the stator 3, the back yoke 2 being provided in contact with or not in contact with the stator 3 to face the surface opposite to the surface where the rotor 5 is provided. The stator 3 is divided into semicircular regions (3a, 3b). A detection coil 4a (referred to as “S1”) and an exciting coil 4b (referred to as “P1”) are wound around side face parts of the regions 3a and 3b, respectively. The rotor 5 is formed of the disk member, and a magnetic plate or a magnetic composite plate having a uniaxial magnetic anisotropy in the planar direction (i.e., the direction of lines shown in FIG. 1C is joined to the rotation shaft 6 at the central point 5a thereof.
A magnetic material having a uniaxial magnetic anisotropy has an easy axis direction in which the magnetic material is easily magnetized and a hard axis direction perpendicular to the easy axis direction and in which the magnetic material is not easily magnetized. In the case of FIGS. 1A to 1C, an up-and-down direction in the figure is the easy axis direction and a right-and-left direction of the figure is the hard axis direction. The magnetic permeability in the easy axis direction is large, and the magnetic permeability in the hard axial direction perpendicular to the easy axis direction is a fraction to a tenth of the magnetic permeability of the easy axis direction, and becomes approximately the same as the magnetic permeability in a vacuum when the magnetic permeability is even smaller.
In this configuration, as the rotor 5 rotates, the easy axis direction of the magnetic anisotropy changes accordingly. A rotation angle can be detected by utilizing this change in the easy axis direction of the magnetic anisotropy. Hereinafter, a principle of detecting the rotation angle will be described.
First, the exciting coil 4b is connected to an alternating-current source 40, and an alternating current is fed to the exciting coil 4b. The alternating current fed to the exciting coil 4b generates a magnetic field in a direction perpendicular to the planar direction when an entire region 3b of the stator 3 is considered on average. In the vicinity of the copper wire of the coil, particularly at a part immediately under the copper wire of the coil, the magnetic field is generated in a direction parallel to the plane and perpendicularly to the copper wire of the coil. An intensity of the magnetic field is much higher than an intensity of the magnetic field at other positions (e.g., the magnetic field at a middle part of the region 3b). That is, a strong magnetic field is generated in a region 30 where the detection coil 4a and the exciting coil 4b are adjacent to each other. By the magnetic field excited by the exciting coil 4b, a voltage corresponding to the magnetic field is generated in the detection coil 4a and a synchronous detection circuit 41 connected to the detection coil 4a detects this voltage.
Here, as the rotor 5 rotates, the above-described easy axis direction changes. An induced voltage is generated in the detection coil 4a by the magnetic force generated by the exciting coil 4b, and since the magnetic field generated by the exciting coil 4b is affected in the easy axis direction of the rotor 5, the voltage induced in the detection coil 4a is affected in the easy axis direction of the rotor 5. That is, the voltage generated in the detection coil 4a changes depending on an angular position of the rotor 5. Using this principle, an angular position (a rotation angle from the reference angle position) of the rotor 5 can be determined from the voltage generated in the detection coil 4a. 
As shown in FIG. 2, the structure of the related art is provided with a shield 7 for shielding an external magnetic field. In order to shield an external magnetic field from at least a radial direction and also shield an external magnetic field from a direction (axial direction) perpendicular to the radial direction, the shield 7 is provided such that an outer edge part is bent to embrace all of the rotor 5, the stator 3 and the back yoke 2.
The back yoke 2 which is formed of an isotropic magnetic thin plate and has substantially the same outer shape as that of the stator 3 is provided in contact with or not in contact with the stator 3 to face the surface opposite to the surface where the rotor 5 is provided. It is not always necessary to provide the back yoke 2, but the back yoke 2 is preferably provided to strengthen magnetic flux coupling.
Here, the back yoke 2 is composed of an isotropic magnetic thin plate, and distortion, a crystal orientation in the thin plate, and the like may cause magnetic anisotropy, which impairs isotropy, and may cause a variation in magnetic permeability. Thus, an output excited by the detection coil is affected and an accuracy of angular detection is decreased. For this reason, the back yoke 2 is not provided in some configurations.
FIG. 3 shows one example of a configuration in which the back yoke is not provided. In FIG. 3, the rotor 5 is composed of a disk of a grain-oriented silicon steel sheet having a uniaxial anisotropy. The stator 3 includes two stators 35 and 36. The stator 35 includes an exciting coil and a detection coil for one phase, and the stator 36 is a coil having the same shape as that of the stator 35. These stators are laminated after being rotated over a predetermined angle. Moreover, a motor 10 including the rotation shaft 6 for rotating the rotor 5 is provided on the side of the stator 3.
In this configuration, there is a case in which the stator 3 is affected by an external magnetic field due to a leakage flux from the motor 10, thereby adversely affecting the accuracy of angular detection. Further essentially, in this configuration, although the bottom surface of the rotor is used in measuring the angle, a leakage magnetic field from the motor affects the bottom surface of the rotor and may disturb the magnetization state. In order to block an external magnetic field, a structure in which a magnetic shield is disposed is effective. However, with the structure shown in FIG. 2 in which the shield embracing the stator and the rotor is provided, the angle detecting apparatus is upsized and cannot be thinned, and the increased number of parts increases costs.
The present disclosure is related to providing an angle detecting apparatus and an angle detecting system having a simple configuration without impairing reduction in thickness and using a resolver capable of reducing the effect of an external magnetic field.